revlog._chunks: inline getchunk

We do this in a somewhat hacky way, relying on the fact that our sole caller
preloads the cache right before calling us. An upcoming patch will make this
more sensible.

For a 20 MB manifest with a delta chain of > 40k, perfmanifest goes from 0.49
seconds to 0.46.

mercurial/revlog.py

@@ -863,17 +863,20 b' class revlog(object):'
         length = self.length
         inline = self._inline
         iosize = self._io.size
-        getchunk = self._getchunk
+        buffer = util.buffer
 
         l = []
         ladd = l.append
 
+        # XXX assume for now that chunkcache is preloaded
+        offset, data = self._chunkcache
+
         for rev in revs:
             chunkstart = start(rev)
             if inline:
                 chunkstart += (rev + 1) * iosize
             chunklength = length(rev)
-            ladd(decompress(getchunk(chunkstart, chunklength)))
+            ladd(decompress(buffer(data, chunkstart - offset, chunklength)))
 
         return l